1. Field of the Invention
The present invention relates to a vertical cavity type semiconductor light emitting device such as a surface emitting laser, and a light emitting apparatus, an optical disk apparatus and a recording apparatus utilizing the same. The present invention also relates to an etching method which can be used for fabricating the vertical cavity type semiconductor light emitting device.
2. Description of the Related Art
A ZnSe type II-VI group compound semiconductor material is a direct transition type semiconductor which has a substantially wide band gap. Thus, the material appears to be suitable for emitting blue laser light. Hence, the development of a semiconductor laser which emits blue laser light (hereinafter, simply referred to as a "blue semiconductor laser") employing the ZnSe type II-VI group compound semiconductor material is actively being performed.
The development of a vertical cavity type semiconductor laser is also conducted which employs a GaAs type III-V group compound semiconductor material. Furthermore, a vertical cavity type blue semiconductor laser is also reported which employs the ZnSe type II-VI group compound semiconductor material.
FIG. 13 is a structural cross-sectional view showing a conventional vertical cavity type surface emitting blue semiconductor laser employing a ZnSe type II-VI group compound semiconductor.
In the illustrated structure of the conventional vertical cavity type surface emitting blue semiconductor laser 1300 in FIG. 13, a Cl-doped n-type ZnSe epitaxial cladding layer 172, a multiple quantum well active layer 173 including ZnCdSe well layers and ZnSe barrier layers, and an N(nitrogen)-doped p-type ZnSe epitaxial cladding layer 174 are sequentially provided on an Si-doped n-type GaAs substrate 171. On the p-type cladding layer 174, a polycrystalline ZnO buried layer 1375 having an opening is provided and functions as a current constricting layer (a current blocking layer). A p-side mirror 177p including a multilayer structure of polycrystalline SiO.sub.2 layers and polycrystalline TiO.sub.2 layers is provided in the opening of the ZnO buried layer 1375. In a window 171a of a substrate 171 provided below the active layer 173, a n-side mirror 177n including a multilayer structure of polycrystalline SiO.sub.2 layers and polycrystalline TiO.sub.2 layers is provided. Furthermore, a p-type AuPd electrode 176 is provided so as to cover the p-side mirror 177p and the ZnO buried layer 1375. An n-type AuGe electrode 178 is provided on the bottom surface of the substrate 171 except for the window 171a.
In the surface emitting blue semiconductor laser 1300 as illustrated in FIG. 13, laser light emitted from the active layer 173 is amplified by using the p-side mirror 177p and the n-side mirror 177n and then is so emitted from the window 171a of the substrate 171 (in the downward direction in FIG. 13).
It is reported that the above-described structure affords a current injection type laser oscillation at a low temperature of 77K (see, for example, Applied Physics Letters, Vol. 66, No. 22, pp. 2929-2931, May 1995).
However, the conventional vertical cavity type blue surface emitting blue semiconductor laser shown in FIG. 13 allows a current to be injected from the p-type electrode 176 to the active layer 173 only through a narrow gap between the p-side mirror 177p and the current block layer 1375. Accordingly, electric resistance for the injected current increases. Moreover, the injected current flows in a spreading manner toward the n-type electrode 178 provided on the bottom surface of the substrate 171, as indicated by the arrows in FIG. 13.
Therefore, light is generated in the active layer 173 not only at a region thereof sandwiched by the p-side mirror 177p and the n-side mirror 177n but also in regions outside the sandwiched region. Thus, an outer portion of the generated light is not oscillated, resulting in no contribution to gain of the laser oscillation. Consequently, light emission efficiency decreases while threshold current density increases.